An 27 liter indoor air sample is collected in a Tedlar bag in the crawl space of a building built on an old municipal dump. There is a suspicion that methylene chloride vapor may be seeping into the building. The temperature is 32¢K and the pressure is 767.6 millimeters of mercury. The expanded bag is returned to the laboratory for analysis and allowed to equilibrate to 25¢J and 760 millimeters of mercury. One milliliter of the sample is withdrawn from the bag with a gastight syringe. The mass of methylene chloride in the 1 ml aliquot is 28£gg. Calculate the concentration in parts per million by volume (ppm) methylene chloride in the air sample at the time of sampling?

Question

An 27 liter indoor air sample is collected in a Tedlar bag in the crawl space of a building built on an old municipal dump. There is a suspicion that methylene chloride vapor may be seeping into the building. The temperature is 32¢K and the pressure is 767.6 millimeters of mercury. The expanded bag is returned to the laboratory for analysis and allowed to equilibrate to 25¢J and 760 millimeters of mercury. One milliliter of the sample is withdrawn from the bag with a gastight syringe. The mass of methylene chloride in the 1 ml aliquot is 28£gg. Calculate the concentration in parts per million by volume (ppm) methylene chloride in the air sample at the time of sampling?

Answer 1

To calculate the concentration of methylene chloride in parts per million by volume (ppm), we need to follow these steps:

Step 1: Convert the volume of the air sample to liters.
The given volume of the air sample is 27 liters, so no conversion is required.

Step 2: Determine the number of moles of methylene chloride in the 1 ml aliquot.
The mass of methylene chloride in the 1 ml aliquot is given as 28 μg. To convert this to grams, divide by 1,000,000.
28 μg = 0.000028 g

Step 3: Convert the mass of methylene chloride to moles.
To convert the mass of methylene chloride to moles, we need to know its molar mass. The molar mass of methylene chloride (CH2Cl2) is approximately 84.93 g/mol.
moles = mass / molar mass
moles = 0.000028 g / 84.93 g/mol

Step 4: Calculate the concentration in moles per liter.
To calculate the concentration in moles per liter, divide the number of moles by the volume of the air sample (27 liters).
concentration (mol/L) = moles / volume (L)
concentration (mol/L) = (0.000028 g / 84.93 g/mol) / 27 L

Step 5: Convert the concentration to parts per million by volume (ppm).
To convert the concentration from moles per liter to parts per million by volume (ppm), we need to multiply by 1,000,000.
ppm = concentration (mol/L) * 1,000,000
ppm = [(0.000028 g / 84.93 g/mol) / 27 L] * 1,000,000

Now you can substitute the values into the equation to calculate the concentration in ppm.